Infrared spectra and the assignment of absorptions. Discuss the impact of mesity
ID: 946600 • Letter: I
Question
Infrared spectra and the assignment of absorptions. Discuss the impact of mesitylene bonding on the CO stretching vibrational mode wavenumber position of the product with respect to the starting Mo(CO)6. Also, discuss the impact of mesitylene binding on the vibrational modes of mesitylene itself, with respect to free mesitylene.
This is lab of Organometallic Synthesis: 0.5 g (~ 1.9 mmol) of Mo(CO)6 was added with 5mL (~36mmol) of mesitylene. The apparatus is assembled in the hood using a straight reflux condenser. The Mo(CO)6 is volatile when heated and will sublime into the condenser during the reaction. Pass nitrogen over the reaction mixture continuously during the reaction. After 25 min, stop reflux When the solution has cooled to room temperature, add 8 mL of hexane to complete the precipitation. Suction filter the solution and rinse the yellow product (that is contaminated with black metallic molybdenum), with 5 mL of hexane. Purify the crude product by dissolving it in a minimum of CH2Cl2(no more than ~ 5 mL). Filter your solution and then add ~15 mL of hexane to the filtrate liquid to precipitate the product. Suction filter off the yellow [1,3,5-C6H3(CH3)3]Mo(CO)3 precipitate.
This is a baseline spectrum, I dunno if I need it, highest peak is around 1855
Explanation / Answer
IR spectroscopy of the product will show two C-O stretches, one of which were accounted for by a strong peak at 1852 cm-1 and the other of which was accounted for by a medium peak at 1942 cm-1. Whereas Mo(CO)6 shows a single stretch at 1982 cm-1.
The coordinated mesitylene will have lower wave numbers with respect to the free mesitylene due to weakening of the pi bonds upon coordination.